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WASHINGTON (AP) — A senior White House official raised the possibility Friday of a broader American military campaign that targets an Islamic extremist group’s bases in Syria, saying the U.S would take whatever action is necessary to protect national security.

“We’re not going to be restricted by borders,” said Ben Rhodes, President Barack Obama’s deputy national security adviser.

The White House said the president has received no military options beyond those he authorized earlier this month for limited airstrikes against the Islamic State group in Iraq and military aid to Iraqi and Kurdish forces. Thus far, the United States has avoided military involvement in Syria’s three-year civil war. But faced with the Islamic State making gains across the region and the beheading of an American journalist, the administration’s resistance may be weakening.

Rhodes spoke a day after Obama’s top military adviser warned the extremists cannot be defeated without “addressing” their sanctuary in Syria.

Many prominent Republicans and some Democrats have called on Obama to hit back harder at the Islamic State militants.

Sen. Marco Rubio, a prospective 2016 presidential candidate, said in an interview Friday that attacking their supply lines, command and control centers and economic assets inside Syria “is at the crux of the decision” for Obama. The risk of “getting sucked into a new war” is outweighed, he said, by the risk of inaction.

To hit back at the group, Obama has stressed military assistance to Iraq and efforts to create a new, inclusive government in Baghdad that can persuade Sunnis to leave the insurgency. He also has sought to frame the Islamic State threat in terms that convince other countries — not just in the Mideast but also in Europe — of the need to create a broad coalition against the extremists.

In an op-ed for The Washington Post, Vice President Joe Biden said the U.S. was prepared to help Iraq pursue a federal system that would decentralize power away from Baghdad. While saying that Iraq is making progress in forming a new government, Biden warned that sectarian divisions were fueling extremist movements like the Islamic State.

Lukman Faily, the Iraqi ambassador to Washington, said in an interview this week that Baghdad’s new leadership has been told to expect additional military help once the new government is seated, possibly in early September. But an Iraqi counteroffensive may yield only temporary gains if the Islamic State retreats to areas of Syria beyond the government’s control.

“The U.S. can’t defeat the Islamic State terrorist army in Iraq if it does not strike its leadership and core base in Syria simultaneously,” said Oubai Shahbandar, a Washington-based senior strategist for the Western-backed opposition Syrian National Coalition group. “A real strategy requires linkage of the military effort in Iraq with Syria,” he said.

Rhodes said the U.S. was “actively considering what’s going to be necessary to deal with that threat.” Speaking on the Massachusetts island of Martha’s Vineyard, where Obama is on vacation, Rhodes said: “We’ve shown time and again that if there’s a counterterrorism threat, we’ll take direct action against that threat, if necessary.”

The recent execution of journalist James Foley could be seen as a turning point in a long-running battle against the group, whose origins are in an al-Qaida offshoot that U.S. forces faced in Iraq several years ago, he said. Foley’s killing, he added, was “an attack on our country.”

Obama faces tough decisions.

He can continue helping Iraqi forces try to reverse the group’s land grabs in northern Iraq by providing more arms and American military advisers and by using U.S. warplanes to support Iraqi ground operations. On Friday, the Pentagon announced that U.S. warplanes made three more airstrikes against Islamic State targets near the Mosul Dam, including a machine gun position that was firing on Iraqi forces.

But what if the militants pull back, even partially, into Syria and regroup, as Defense Secretary Chuck Hagel on Thursday predicted they would, followed by a renewed offensive?

“In a sense, you’re just sort of back to where you were,” said Robert Ford, a former U.S. ambassador to Syria who quit in February in disillusionment over Obama’s unwillingness to arm moderate Syrian rebels.

“I don’t see how you can contain the Islamic State over the medium term if you don’t address their base of operations in Syria,” he said in an interview before intensified U.S. airstrikes this week helped Kurdish and Iraqi forces recapture the Mosul Dam.

Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, said Thursday the Islamic State militants can be contained only so long and at some point their Syrian sanctuary will have to be dealt with.

“Can they be defeated without addressing that part of their organization which resides in Syria? The answer is no,” he told a Pentagon news conference where Hagel called the group a dire threat that requires an international, not just an American, response.

“That (sanctuary) will have to be addressed on both sides of what is essentially at this point a nonexistent border,” Dempsey added. “And that will come when we have a coalition in the region that takes on the task of defeating ISIS over time,” he said, using an alternate acronym for the group. “ISIS will only truly be defeated when it’s rejected by the 20 million disenfranchised Sunni that happen to reside between Damascus and Baghdad.”

Just in Iraq, Obama has difficult choices to make. Its sectarian divisions and political dysfunction created the opening that allowed Islamic State fighters to sweep across northern Iraq in June, capturing U.S.-supplied weapons that Iraqi forces left behind when they fled without a fight.

Among his options:

—Sending more troops to Baghdad to strengthen security for the U.S. Embassy, as requested by the State Department. Officials said the number under consideration is fewer than 300. They would be in addition to several hundred U.S. troops already in the capital helping to protect U.S. facilities and personnel.

—Speeding up the arming of Iraqi and Kurdish forces. The administration has been supplying Iraqi government forces with Hellfire missiles, small arms and ammunition, but critics say the pace is too slow.

—Increasing the number and expanding the role of the dozens of U.S. military advisers coordinating with Iraqi forces in Baghdad and the Kurdish capital of Irbil. They could be given more direct roles in assisting Iraqis on the ground by embedding with units in the field or scouting targets for U.S. airstrikes.